float x = 250.0;          // half the width of the window CHANGE
float y = 500;            // full height size of window   CHANGE
float w = 0;              // width of rectangle frame at start
float h = 0;              // starting position of image window [y-axis].

float imageWidth = 400 - 1;   // image width  CHANGE [-1 needed to center image at end].
float imageHeight = 300 - 1;  // image height CHANGE [-1 needed to center image at end].

void setup () {
  size (500, 500);        // window size
  background (0);
}

void draw () {
  frameRate (600);
    
  if (w > imageWidth) {                          
    if (y < imageHeight) {
      { PImage a;                                     // Declare variable "a" of type PImage
        a = loadImage("brainCoral.jpg");               // Load the images into the program
        image (a, x + 1, h);                          // positions image (a, x-pos, y-pos, x-size, y-size).
      }
    } else {
      rect (x, h, w, y);
      h = h + 1;
      y = y - 2;
      } 
  } else {
     rect (x, 0, w, height);
      x = x - 1;
      w = w + 2;
  }   
}